[gtkmm-documentation] Require C++11

[Kjell Ahlstedt <kjellahl src gnome org>]

commit 35554d5b4bc15aae71d76ae827259cc3113b520a
Author: Kjell Ahlstedt <kjell ahlstedt bredband net>
Date:   Wed Jul 15 19:22:38 2015 +0200

    Require C++11
    
    * configure.ac: Use MM_AX_CXX_COMPILE_STDCXX_11 from mm-common to check for
    compiler support for C++11 and use it (-std=c++11 for current versions of g++).
    Among other reasons, this is because libsigc++ and glibmm now require C++11,
    and gmmproc generates C++11 code.

 configure.ac |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 20515a9..2417dec 100644
--- a/configure.ac
+++ b/configure.ac
@@ -15,7 +15,11 @@ m4_ifdef([AM_SILENT_RULES], [AM_SILENT_RULES])
 AM_MAINTAINER_MODE
 AC_ARG_VAR([ACLOCAL_FLAGS], [aclocal flags, e.g. -I <macro dir>])
 
+MM_PREREQ([0.9.8])
+
 AC_PROG_CXX
+MM_AX_CXX_COMPILE_STDCXX_11([noext],[mandatory])
+
 AC_PATH_PROG([PERL], [perl], [perl])
 AC_PROG_SED